Note: Descriptions are shown in the official language in which they were submitted.
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
NON-CONTACT SENSING SYSTEM
BACKGROUND
[0001] The present invention relates to a non-contact sensor. More
specifically, the present
invention relates to a non-contact sensor that is applied in a mail sorting
facility.
[0002] Mail is sorted and delivered to locations all over the world every day.
Often, mail is
automatically processed by mail sorting equipment to expedite delivery. For
example, a large
stack of letters can be separated by a pick off feeder, which then feeds the
separated letters into
mail sorting equipment at a predetermined rate (e.g., 10-12 pieces per second)
and with a
predetermined pitch or letter separation (e.g., approximately two to three
inches). In some
instances, a "double feed" condition may occur, in which two pieces of mail
are fed into the mail
sorting equipment by the pick off feeder simultaneously and without the proper
separation
between each piece. The double feed can result in a mis-sorting of the mail
pieces, because the
mail sorting equipment downstream of the pick off feeder cannot properly
recognize or track the
double-fed mail.
SUMMARY
[0003] In one embodiment, a non-contact sensing system for detecting a double
feed
condition of mail includes a mail sorting machine having a conveyor, a non-
contact sensor, and a
controller. The mail sorting machine moves the mail, while the non-contact
sensor is positioned
proximate to the conveyor and generates a signal indicative of a thickness of
the mail. The
controller receives the signal from the non-contact sensor and generates an
output signal
indicative of a double feed condition.
[0004] In another embodiment, a method of calculating the likelihood of a
double feed
condition of mail includes generating a thickness profile for the piece of
mail. The thickness
profile is then compared to a historical thickness profile. The historical
thickness profile is based
on a previously generated thickness profile. Finally, a confidence value
associated with the
likelihood of a double feed condition is calculated. The confidence value is
at least partially
based on a comparison of the thickness profile to the historical thickness
profile.
1
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
[0005] In another embodiment, a method of calculating the likelihood of a
double feed
condition of mail includes generating a thickness profile of the mail piece. A
first distinct
thickness and a second distinct thickness are then identified within the
generated thickness
profile of the mail. A transition between the first distinct thickness and the
second distinct
thickness is assigned a position value, and the thickness profile includes at
least two position
values. Finally, a double feed condition is identified based on the at least
two position values.
[0006] In another embodiment, a method of generating a double feed thickness
profile for
detecting a double feed condition includes measuring the thickness and length
of potentially
overlapping pieces of mail with a non-contact sensor; generating a historical
length that is based
at least partially on previously measured lengths of mail; calculating an
offset value between the
potentially overlapping pieces of mail; and generating a thickness profile of
the potentially
overlapping pieces of mail that is based at least partially on the offset
value.
[0007] Other aspects will become apparent by consideration of the detailed
description and
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Fig. 1 is a block diagram of portions of a non-contact double feed
detection system
according to an embodiment of the invention.
[0009] Fig. 2A is a top schematic view of a non-contact double feed detection
system
according to an embodiment of the invention.
[0010] Fig. 2B is another top schematic view of a non-contact double feed
detection system
according to an embodiment of the invention.
[0011] Fig. 2C is yet another top schematic view of a non-contact double feed
detection
system according to an embodiment of the invention.
[0012] Fig. 3 is a flow diagram of one method of determining a double feed
condition.
[0013] Fig. 4 is a flow diagram of another method of determining a double feed
condition.
2
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
[0014] Fig. 5 is a flow diagram that generates a double feed thickness
profile.
[0015] Fig. 6 schematically illustrates two overlapping pieces of mail having
delta values
applied to the mail edges.
[0016] Fig. 7A schematically illustrates two overlapping pieces of mail.
[0017] Fig. 7B schematically illustrates an add-on thickness profile for the
overlapping
pieces of mail shown in Fig. 7A.
DETAILED DESCRIPTION
[0018] Before any embodiments of the invention are explained in detail, it is
to be
understood that the invention is not limited in its application to the details
of construction and the
arrangement of components set forth in the following description or
illustrated in the following
drawings. The invention is capable of other embodiments and of being practiced
or of being
carried out in various ways. Also, it is to be understood that the phraseology
and terminology
used herein is for the purpose of description and should not be regarded as
limiting. The use of
"including," "comprising," or "having" and variations thereof herein is meant
to encompass the
items listed thereafter and equivalents thereof as well as additional items.
Unless specified or
limited otherwise, the terms "mounted," "connected," "supported," and
"coupled" and variations
thereof are used broadly and encompass both direct and indirect mountings,
connections,
supports, and couplings. Further, "connected" and "coupled" are not restricted
to physical or
mechanical connections or couplings.
[0019] Fig. 1 illustrates portions of a non-contact double feed detection
system 10. The
double feed detection system 10 includes a mail sorting machine 14 having at
least one pulley or
roller 18, an inner belt 22, and an outer belt 26, which can be used to move
and/or sort mail 30.
The double feed detection system 10 also includes a non-contact displacement
sensor 34 having
a sensing unit 38, a power/communication cable 42, and a bracket 46. In other
embodiments, the
non-contact double feed detection system 10 may include more or fewer
components than those
shown in Fig. 1. For example, in an embodiment, as shown in Figs. 2A-2C, an
additional sensor
can be added to the non-contact double feed detection system 10.
3
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
100201 The mail sorting machine 14 can be configured a variety of ways to
route and move
the mail 30 through a mail sorting facility. In the embodiment shown in Fig.
1, the mail sorting
machine 14 holds or pinches the mail 30 between the inner belt 22 and the
outer belt 26. In some
embodiments, the inner belt 22 and the outer belt 26 are relatively flexible,
such that they bend
around the edges of the mail 30, holding the mail piece in position as it is
transported through the
mail sorting facility. The rollers 18 are used to support and drive the inner
belt 22 and outer belt
26 at approximately equal speeds to move the pinched mail pieces 30. In other
embodiments, the
mail sorting machine 14 may include different rollers, belts, chains,
conveyors, drive systems,
and the like that are used to move mail 30 through the mail sorting facility.
[0021] As shown in Fig. 1, the sensing unit 38 of the displacement sensor 34
is positioned
near the outer belt 26, and near the roller 18. The sensing unit 38 is secured
in place by the
bracket 46 and powered by the power/communication cable 42. By securing the
sensing unit 38
near the roller 18, the roller 18 can provide a suitable and stable
environment for taking
displacement measurements. For example, the relatively hard surface of the
roller 18 ensures
that the inner belt 22 and the outer belt 26 will pass over the roller 18
without a significant
amount of lateral movement which may otherwise compromise the accuracy of the
measurements made by the sensing unit 38.
[0022] In operation, the sensing unit 38 transmits a signal 50 toward the
outer belt 26. The
signa150 is then reflected off of the outer belt 26 and returned to the
sensing unit 38.
Consequently, the sensing unit 38 can accurately measure and calculate the
distance between the
outer belt 26 and the sensing unit 38, as well as generate a corresponding
output signal. The
output signal can then be transmitted to a controller (as described in greater
detail with respect to
Figs. 2A-2C) via the power/communication cable 42. In some embodiments, the
sensing unit 38
is a photoelectric or laser sensor (e.g., a Baumer OADM 1216460/S35A
photoelectric array
sensor) that transmits and receives a focused beam of light (e.g., a laser),
and generates a
corresponding analog signal that is proportional to the reflection distance of
the light. In other
embodiments, the sensing unit 38 may be another reflective, optical,
inductive, capacitive,
ultrasonic, or other type of non-contact sensor that has the ability to
measure the distance
between the sensing unit 38 and the outer belt 26 to a sufficient degree of
accuracy and generate
an analog or digital signal indicative of that distance.
4
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
[0023] Figs. 2A-2C are top views of the non-contact double feed detection
system 10 shown
in Fig. 1. The embodiments shown in Figs. 2A-2C also include an item present
detect ("IPD")
sensing unit 60 (hereinafter referred to as "IPD") and a controller 64. The
IPD 60 is positioned
upstream of, or prior to the displacement sensor 34. The IPD 60 may include a
variety of
suitable sensors, including non-contact or mechanical displacement sensors
that are capable of
detecting the presence of an object. For example, in one embodiment, the IPD
60 includes a
photocell that uses light to detect the presence of the mail 30. More
specifically, in the
embodiment shown in Figs. 2A-2C, the IPD 60 includes a photocell that is
positioned several
inches upstream of the displacement sensing unit 38 that generates a signal as
the mail 30 passes.
In some embodiments, the signal generated by the IPD 60 is linked to the
displacement sensing
unit 38, and causes the displacement sensing unit 38 to toggle on and off
according to the
position of the mail 30. For example, as the leading edge of the mail 30
passes by the IPD 60,
the IPD 60 generates a signal that is used to "trigger" or turn on the
displacement sensing unit
38. The displacement sensing unit 38 then begins to measure the distance
between the sensing
unit 38 and the outer belt 26. In some embodiments, the signal that is
generated by the IPD 60 is
first received by the controller 64, and the controller 64 uses that signal to
trigger the
displacement sensing unit 38 via the power/communication cable 42. In other
embodiments, the
IPD 60 and the displacement sensing unit 38 may interact in a different manner
(e.g., a direct
connection between the IPD 60 and the sensing unit 38).
[0024] As described above, the controller 64 is electronically linked to both
the displacement
sensing unit 38 and the IPD 60. In some embodiments, the controller 64 is a
conventional
personal computer ("PC") that includes a data acquisition card 68 (e.g., a DAQ
NI DAQ6013
PCI card). In other embodiments a different type of controller 64 may be
implemented. For
example, a programmable logic controller ("PLC") or other controller unit
capable of receiving
input signals and generating output signals may be employed. As described in
greater detail
below, the controller 64 communicates with both the IPD 60 and the
displacement sensing unit
38 to generate an appropriate output 72, if the output 72 is required. The
output 72 can include,
for example, an audible and/or visual alert (e.g., a beeping sound, a flashing
light, etc.).
Alternatively or additionally, the output 72 may affect the mail sorting
equipment downstream of
the displacement sensor 34, for example, by removing or culling out double-fed
mail.
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
[0025] Referring now to Fig. 2A, the mail 30 is shown prior to, or upstream of
the
displacement sensing unit 38. As previously described, the inner belt 22 and
the outer belt 26 of
the mail sorting machine 14 are relatively flexible such that conform to the
shape of the mail 30,
which creates a protrusion (e.g., a protrusion relative to the portion of the
inner belt 22 and the
outer belt 26 that is not holding the mail 30) that can be detected by the
displacement sensing
unit 38. The leading edge of a protrusion (and the corresponding piece of mail
30) is detected by
the IPD 60, which transmits a signal to the controller 64 indicating that the
mail 30 is present.
The controller 64 receives this signal and triggers the displacement sensing
unit 38.
Additionally, the controller 64 begins to sample the signals generated by the
displacement
sensing unit 38 via the data acquisition card 68. For example, in some
embodiments, the data
acquisition card 68 receives the analog signal from the displacement sensing
unit 38 such that
approximately 200 samples can be gathered per piece of mail 30. The data
acquisition card 68
then converts the analog signal to a digital signal and conditions the digital
signal so that the
controller 64 can create a thickness profile of the mail piece 30. The
thickness profile is related
to the thickness of the protrusion (and corresponding mail 30) along the
length of the protrusion
(and corresponding mail 30).
[0026] Fig. 2B shows mai130 positioned near the displacement sensing unit 38.
As
described above, the displacement sensing unit 38 measures the deflection
distance of the outer
belt 26, which is used by the controller 64 and the data acquisition card 68
to generate a
thickness profile. In the embodiment shown in Fig. 2B, as the mail 30 passes
in front of the
displacement sensing unit 38 the controller 64 generates a thickness profile
that corresponds to a
single piece of mail. For example, the thickness profile that is generated in
Fig. 2B has a single
increase or step, a continuous and relatively constant raised portion, and a
single step down. As
described with respect to Figs. 3-5, the thickness profile can be used to
generate the output 72, if
the output 72 is required. For example, if the thickness profile corresponds
to a single piece of
mail (i.e., no double feed condition is detected), the controller 64 may not
generate the output 72.
Alternatively, the controller 64 may generate an audible and/or visual output
72 indicating that
the thickness profile corresponds to a single piece of mail 30 (e.g., lighting
a green light on a
light tree).
6
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
[0027] Fig. 2C also shows mail 30 positioned near the displacement sensing
unit 38.
However, in the embodiment shown in Fig. 2C, a double feed condition exists.
Specifically, two
pieces of overlapping mail 30 are positioned near the displacement sensing
unit 38. As the
overlapping pieces of mail 30 pass in front of the displacement sensing unit
38, a thickness
profile is generated that corresponds to a double feed condition. As described
with respect to
Figs. 3-5, there are a variety of ways to identify a thickness profile that
corresponds to a double
feed condition. After identifying that a double feed condition has occurred,
the controller 64
may initiate an audible and/or visual signal output 72 indicating that a
double feed condition
exists. Alternatively or additionally, the controller 64 may remove the mail
30 that has been
identified as being double-fed.
[0028] Fig. 3 illustrates an exemplary process 100 that detects a double feed
condition. In
some embodiments, the process 100 is executed by the controller 64 to generate
the output 72.
As such, while executing the process 100, the controller 64 may generate or
return a double feed
confidence factor, which can then be utilized to generate the output 72. For
example, in one
embodiment, the controller 64 generates a double feed confidence factor that
is based on a three
point scale (e.g., zero is a low double feed confidence, indicating there is
no double feed
condition present; three is a high double feed confidence, indicating that a
double feed condition
is likely). In such an embodiment, the controller 64 may not initiate the
output 72 if the double
feed confidence factor is zero, but may initiate the output if the double feed
confidence factor is
three.
[0029] The process 100 begins by inputting a thickness profile for a new piece
of mail
("TP") (step 104). As previously described, a thickness profile is related to
the thickness of the
mail 30 along its length. Accordingly, the thickness profile is input after
the displacement
sensing unit 38 measures the thickness of the mail 30 along the length of the
mail 30 (see Figs.
2A-2C). A maximum expected envelope length value ("MaxL") and a minimum
expected
envelope length value ("MinL") are also input during step 104. The process 100
continues by
verifying that the length of the thickness profile of the new piece of mail
(TP) is greater than the
MinL value (step 108). If the length of the TP is not greater than the MinL
value, the process
100 returns a double feed confidence of zero (e.g., if the length is less than
the minimum length,
a double condition cannot exist)(step 112). If, however, the length of the
thickness profile is
7
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
greater than the MinL value, the next step in the process 100 is to verify
that there are at least
three unique thickness points along the length of the TP (step 116). Verifying
that there are at
least three unique thickness points along the length of the TP confirms that
there are at least two
pieces of mail that are overlaid, with the thickest profile being the overlaid
portion. If there are
not at least three unique thickness points, the process 100 returns a double
feed confidence of
zero (step 120), indicating that a double feed condition has not occurred.
[0030] If there are at least three unique thickness points along the length of
the TP, the next
step in the process 100 is to build an array of difference values or "deltas"
along the length of the
TP (step 124). As shown in Fig. 6, for example, for two overlapping pieces of
mail there may be
a first delta or thickness step (D 1) at the beginning of the overlapping
portion, and a second delta
or thickness step (D2) at the end of the overlapping portion. After the array
of deltas is
generated, the next step in the process 100 is to verify that there is a delta
that matches the
inverse of another delta (step 128). As shown in Fig. 6, for example, the
delta (D1) and the delta
(D2) are inverses or mirror images of one another. If there is not a delta
that is an inverse of
another delta (e.g., a "delta pair"), the process 100 returns a double feed
confidence factor of one
(step 132). The double feed confidence factor of one is returned because,
while there were three
unique thickness points identified in step 116, the delta values corresponding
to those unique
thickness points are not expected (i.e., a delta pair is not recognized),
indicating inconsistent
measurements. In some embodiments, a double feed confidence factor of one may
be a signal of
inaccurate measurements or faulty equipment.
[0031] If there is at least one valid delta pair, the process 100 continues by
relating the delta
values and the physical dimensions of the overlapping mail pieces (step 136).
As shown in Fig.
6, for example, the beginning of mail piece 405 begins at delta (D 1), while
the end of mail piece
400 ends at delta (D2). Correspondingly, the beginning of the overlapping
portion of mail
begins at delta (D 1), while the end of the overlapping portion of mail ends
at delta (D2). Using
the related delta and mail dimension data, the process 100 continues by
calculating the
dimensions of each mail piece (step 140). For example, the dimensions of the
mail piece 400
can be calculated by subtracting the delta (D2) from the length of the TP
(i.e., MailPieceOne =
Length(TP) - D2). Additionally, the dimensions of the mail piece 405 can be
calculated by
subtracting the delta (D 1) from the length of the TP (i.e., MailPieceTwo =
Length(TP) - D 1).
8
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
After the dimensions of each piece have been calculated, the process 100
continues by verifying
that the lengths of the mail pieces 400 and 405 are greater than the minimum
mail piece size
(MinL) (step 144), which may aid in verifying that the length values are
accurate and a valid
double feed condition has been identified. If either of the mail pieces is
shorter than the
minimum, the process 100 returns a double feed confidence factor of one (step
148). The double
feed factor of one corresponds to a situation in which three unique thickness
points were
identified (step 116), but one or both of the first and second mail pieces is
shorter than the
minimum value MinL, which may indicate erroneous, invalid, and/or inconsistent
measurements.
When the process 100 returns a double feed confidence factor of one, the
mai130 may be culled
out. Alternatively, the mail 30 may be rerouted through the mail sorting
machine, or an audible
or visual signal may also be used to indicate that erroneous, invalid, or
inconsistent
measurements have been identified. However, if each of the mail pieces is
longer than the
minimum mail piece size (MinL), the process 100 returns a double feed
confidence factor of two.
[0032] Fig. 4 illustrates another exemplary process 200 that can be used to
identify a double
feed condition. The process 200 may be most efficiently implemented if the
mail stream is
relatively uniform in size and shape. For example, the process 200 may be the
most efficient at
detecting a double feed condition if the mai130 in the mail stream is, for
example, a bulk mailing
or other type of mass mailing (e.g., a large group of flyers, credit card
offerings, insurance
offerings, etc.). As described in greater detail below, the process 200
generally includes steps
which compare a thickness profile from the mail 30 to a "historical" or
previously stored
thickness profile.
[0033] The process 200 begins by inputting a thickness profile for a new piece
of mail (step
204). As previously described, the thickness profile for a new piece of mail
can be created from
the data provided by the displacement sensing unit 38. After a thickness
profile has been created
and input, the process 200 continues by checking if there is a "historical"
thickness profile (step
208). A historical thickness profile is a thickness profile that has already
been created and stored
in the controller 64 (see Figs. 2A-2C), and that corresponds to a previously
sorted size and type
of mail piece 30. The historical thickness profile can then by utilized as a
standard or expected
thickness profile for that size and type of mail 30 in the future. As a
result, if the same size and
9
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
type of mail is repeatedly run, the controller 64 has a standard thickness
profile for that size and
type of mail, as described in greater detail below.
[0034] If a historical thickness profile has not yet been created, the
thickness profile of the
new mail type is temporarily stored so that a new historical profile can be
created (step 212).
After a certain number of matching thickness profiles is temporarily stored, a
new historical
profile is created (also step 212). For example, a new historical profile may
be created after five
new and matching thickness profiles are consecutively stored. The number of
matching
thickness profiles that are needed to create a new historical thickness
profile is a configurable
value, and is generally large enough to provide confidence that the historical
thickness profile
represents the thickness profile of the current mail stream. After the new
historical profile is
created, or is in the process of being created (step 212), the process 200
returns a double feed
confidence factor of zero (step 216). If a double feed condition interrupts
the creation of a new
historical thickness profile (e.g., overlapping mail passes by the
displacement sensing unit 38
after only three matching thickness profiles), the mail pieces with the non-
matching thickness
profile may be culled out, and the process 200 may start over.
[0035] If a historical thickness profile has already been created (and
confirmed in step 208),
the process 200 continues by comparing the new thickness profile to the
historical profile (step
220). If the new thickness profile matches the dimensions of the historical
thickness profile, the
process 200 assumes that a double feed condition has not occurred and returns
a double feed
confidence factor of zero (step 224). However, if the new thickness profile
does not match the
historical thickness profile, the next step in the process 200 is to generate
an expected double
feed thickness profile (step 228). As described in greater detail with respect
to Fig. 5, generating
an expected double feed thickness profile may include, for example, verifying
that the total
length of the new thickness profile is not greater than two times the length
of the historical
thickness profile, and calculating the offset between the two overlapping
pieces of mail 30.
After generating the expected double feed profile (see Fig. 5) (step 228), the
process 200
continues by checking if the expected double feed thickness profile matches
the new thickness
profile (step 232). If the expected double feed thickness profile and the new
thickness profile
match, a double feed confidence of three is returned (step 236). Returning a
double feed
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
confidence of three may lead to an audible or visual indication as well as the
removal of the
double feed from the mail stream.
[00361 However, if the generated double feed thickness profile does not match
the new
thickness profile, the historical thickness profile used to create the double
feed thickness profile
in step 228 is invalidated (step 240). The process 200 continues by
temporarily storing the new
thickness profile so that a new historical thickness profile can be created as
described above with
respect to step 212. In other embodiments, the process 200 may have more or
fewer steps than
those shown in Fig. 4. For example, in an alternative embodiment, the process
200 may be
abbreviated, such that expected double feed profile 228 is not calculated.
Rather, if the new
thickness profile does not match the historical thickness profile, the process
200 returns a double
feed confidence factor of three. Other variations of the process 200 are also
possible.
[0037] Fig. 5 illustrates an exemplary process 300 that can be used to
generate a double feed
thickness profile. The process 300 assumes that a historical thickness profile
has been created,
for example, using the process 200 shown in Fig. 4. The process 300 then
creates a double feed
thickness profile based on the current historical thickness profile and a
length constant (L). The
first step in the process 300 is to input the length of the "new" double feed
thickness profile to
generate a length constant (L) (step 304). As applied to the double feed
detection process 200
described in Fig. 4, the length of the new double feed profile is analogous to
the "new" thickness
profile that is used in step 220.
[0038) The process 300 continues by verifying that the length (L) is a viable
value (step
308). For example, the length (L) of the double feed profile must be greater
than or equal to the
historical profile length ("HPL") (i.e., the double feed cannot be shorter
than a single piece of
mail). Additionally, the length (L) of the double feed must also be smaller
than two times the
HPL (i.e., the double feed cannot be longer than two pieces of mail). If
either of the conditions
set forth in step 308 is not true, the process 300 ends (step 312) and returns
an empty or null
double thickness profile (i.e., the length (L) is invalid and a double feed
thickness profile cannot
be generated). However, if the length (L) is greater than or equal to the HPL,
and the length (L)
is less than two times the HPL, the process 300 continues by calculating the
offset between the
pieces of mail 30 (step 316). The offset is approximately equivalent to the
amount or length of
11
CA 02564245 2006-10-17
Attorney Docket No. 061151-9019
one piece of mail that extends beyond the other piece of mail (e.g., offset =
length (L) - HPL), if
the overlapping mail pieces are not stacked directly on top of one another.
For example, as
shown in Fig. 7A, the leading edge of the first piece of mail 500 begins at
zero. Accordingly, the
leading edge of the second piece of mai1505 begins at the offset mark.
[0039] The process 300 continues by generating an "add-on" thickness profile
(step 320).
The add-on thickness profile is of length (L), and has a value of zero between
the zero mark and
the offset value, as shown in Fig. 7B. As also shown in Fig. 7B, the add-on
thickness profile has
a value that is equal to the historical thickness profile from the offset
value to the length (L).
Combining the add-on thickness profile and the historical thickness profile
yields the expected
double feed profile (step 324). After the add-on and historical thickness
profiles have been
combined, the process 300 ends by returning the generated double feed
thickness profile (step
328). In some embodiments, the double feed thickness profile is utilized by
another process, for
example, the process 200 shown in Fig. 4.
[0040] In some embodiments, the controller 64 can switch from one process to
another
and/or complete multiple processes, such as those described with respect to
Figs. 3-5,
concurrently. For example, in one embodiment, the controller 64 begins by
completing both the
processes 100 and 200 concurrently. In such an embodiment, the process 100 is
utilized to detect
a double condition, while the process 200 generates a historical thickness
profile (see step 212 of
the process 200). Then, after a historical thickness profile is generated, the
controller 64 utilizes
the process 200 to detect a doubles condition. Other variations and process
combinations are
also possible.
[0041] Various embodiments of the invention are set forth in the following
claims.
12
